Control circuit, control method used in PFC circuit and power source system thereof

ABSTRACT

A control circuit, control method used in a PFC circuit and the power source system thereof are disclosed herein. The control circuit comprises: a zero current detection circuit having a polarity detection circuit for outputting a first and a second digital signals and a signal conversion circuit for generating an analog signal; a feedback circuit for generating a driving pulse signal; and a pulse distribution circuit for distributing the driving pulse signal to a first and a second switches according to the first and the second digital signal. After a switch cycle, one of the first and the second switch performs an ON operation for the next switch cycle when the current flowing through the inductor decreases to a predetermined threshold value, wherein an ON time of the first switch is equal in each switch cycle, and an ON time of the second switch is equal in each switch cycle.

RELATED APPLICATIONS

This application claims priority to Chinese Application Serial Number201210284439.2, filed Aug. 6, 2012, which is herein incorporated byreference.

BACKGROUND

1. Field of Invention

The present invention relates to the technical field of powerelectronics. More particularly, the present invention relates to acontrol circuit, control method used in a PFC circuit and the powersource system including the control circuit.

2. Description of Related Art

Currently, in order to reduce the serious harmonic pollution to a powergrid caused by frequently-used power electronic devices, generally thereis a need to introduce a power factor correction (PFC) circuit, so as tomake the input current harmonic meet the requirements of a predeterminedharmonic through the PFC circuit. Additionally, the development trend ofthe PFC circuit is towards the direction of high efficiency and highpower density, just as most of the power source products.

Taking a bridgeless PFC circuit topology as an example, the circuit hasmany advantages, such as low conduction losses, low common-modeinterfere and high utilization ratio of components. For example, thebridgeless PFC circuit includes a first bridge arm and a second bridgearm connected with each other in parallel. The first bridge arm isformed by a first MOSFET and a second MOSFET. The second bridge arm isformed by a first diode D1 and a second diode D2.

When the second MOSFET is off and the first MOSFET is on in the firstbridge arm, the inductor releases energy through the first MOSFET and afourth MOSFET. Accordingly, the inductor current decreases. Afterwards,the inductor current decreases to zero at a certain moment and after themoment the direction of the current is reversed. When the first MOSFETis off, a voltage (V_(DS)) across two ends of the drain electrode andthe source electrode of the second MOSFET starts to decrease. If thesecond MOSFET is controlled to be turned on when the voltage decreasesto zero, it is realized to turn on the second MOSFET under a zerovoltage, so as to reduce the switch loss. However, it is a subject forrelated technicians to solve which control mechanism is used to realizethe above-mentioned turn-on under the zero voltage so as to reduce theswitch loss of the circuit. Additionally, it is a task for designers tosolve how the zero-crossing point of the inductor current isautomatically detected in a simple and effective way.

SUMMARY

For the above-mentioned defects of a bridgeless PFC circuit of theconventional art in terms of reducing the switch loss, the presentinvention provides a control circuit, control method used in a PFCcircuit and the power source system including the control circuit.

According to a technical aspect of the present invention, a controlcircuit used in a PFC circuit is provided. The PFC circuit includes aninductor, a first bridge arm and a second bridge arm connected to thefirst bridge arm in parallel. The first bridge arm has a first switchand a second switch connected with each other in series. The common nodeof the first switch and the second switch is coupled to an input voltagethrough the inductor.

The control circuit includes a zero current detection circuit, afeedback circuit and a pulse distribution circuit. The zero currentdetection circuit includes a polarity detection circuit and a signalconversion circuit. The polarity detection circuit is used to receive aninput voltage and output a first digital signal and a second digitalsignal indicating a polarity of the input voltage. A potential of thefirst digital signal is opposite to that of the second digital signal.The signal conversion circuit receives at least one inductive signalreflecting an inductive voltage of the inductor, the first digitalsignal and the second digital signal and generates an analog signal. Thefeedback circuit is used to receive the analog signal and apredetermined pulse signal and generate a driving pulse signal. Thepulse distribution circuit is used to distribute the driving pulsesignal to the first switch and the second switch of the first bridge armaccording to the first digital signal and the second digital signal sothat one of the first switch and the second switch performs an ONoperation. After a switch cycle, one of the first switch and the secondswitch performs the ON operation for the next switch cycle when thecurrent flowing through the inductor decreases to a predeterminedthreshold value, wherein an ON time of the first switch is equal in eachswitch cycle, and an ON time of the second switch is equal in eachswitch cycle.

According to another technical aspect of the present invention, a powersource system is provided. The power source system includes a PFCcircuit and a control circuit. The PFC circuit includes: a first bridgearm and a second bridge arm. The first bridge arm includes a firstswitch and a second switch connected with each other in series. Thecommon node of the first switch and the second switch is coupled to oneend of an input voltage through an inductor. The second bridge armincludes a third switch and a fourth switch connected with each other inseries. The common node of the third switch and the fourth switch iscoupled to the other end of the input voltage. The control circuitincludes: a zero current detection circuit having a polarity detectioncircuit and a signal conversion circuit, a feedback circuit and a pulsedistribution circuit. The polarity detection circuit is used to receivethe input voltage and output a first digital signal and a second digitalsignal indicating the polarity of the input voltage. A potential of thefirst digital signal is opposite to that of the second digital signal.The signal conversion circuit receives at least one inductive signalreflecting an inductive voltage of the inductor, the first digitalsignal and the second digital signal and generates an analog signal. Thefeedback circuit is used to receive the analog signal and apredetermined pulse signal and generate a driving pulse signal. Thepulse distribution circuit is used to distribute the driving pulsesignal to the first switch and the second switch of the first bridge armaccording to the first digital signal and the second digital signal, sothat the first switch or the second switch performs an ON operation.After a switch cycle, one of the first switch and the second switchperforms an ON operation for the next switch cycle when the currentflowing through the inductor decreases to a predetermined thresholdvalue, wherein an ON time of the first switch is equal in each switchcycle, and an ON time of the second switch is equal in each switchcycle.

According to a further technical aspect of the present invention, acontrol method used for a PFC circuit is provided. The PFC circuitincludes an inductor, a first bridge arm and a second bridge armconnected to the first bridge arm in parallel. The first bridge arm hasa first switch and a second switch connected with each other in series.The common node of the first switch and the second switch is coupled toan input voltage through the inductor. The control method includes thefollowing steps: (a) detecting a polarity of the input voltage so as tooutput a first digital signal and a second digital signal indicating thepolarity of the input voltage; (b) generating an analog signal throughthe signal conversion processing according to at least one inductivesignal reflecting an inductive voltage of the inductor, the firstdigital signal and the second digital signal; (c) providing apredetermined pulse signal and generating a driving pulse signalaccording to the analog signal and the predetermined pulse signal; and(d) distributing the driving pulse signal to the first switch and thesecond switch according to the first digital signal and the seconddigital signal so that one of the first switch and the second switchperforms an ON operation.

According to yet a further technical aspect of the present invention, acontrol circuit used for the PFC circuit is provided. The PFC circuitincludes an inductor, a first bridge arm and a second bridge armconnected to the first bridge arm in parallel. The first bridge arm hasa first switch and a second switch connected with each other in series.The common node of the first switch and the second switch is coupled toan input voltage through the inductor. The control circuit includes azero current detection circuit, a feedback circuit and a pulsedistribution circuit. The zero current detection circuit includes anedge detection circuit which is used to receive at least one inductivesignal reflecting an inductive voltage of the inductor and detect andoutput a rising edge or a falling edge in the inductive signal; and anenabling circuit which is used to filter the detected rising edge or thedetected falling edge and output a zero current detection signal. Thefeedback circuit is used to receive the zero current detection signaland a predetermined pulse signal and generate a driving pulse signal.The pulse distribution circuit includes a polarity detection circuit.The polarity detection circuit receives the input voltage and outputs afirst digital signal and a second digital signal indicating a polarityof the input voltage. A potential of the first digital signal isopposite to that of the second digital signal. The pulse distributioncircuit distributes the received driving pulse signal to the firstswitch and the second switch of the first bridge arm according to thefirst digital signal and the second digital signal so that one of thefirst switch and the second switch performs an ON operation. After aswitch cycle, one of the first switch and the second switch performs theON operation for the next switch cycle when the current flowing throughthe inductor decreases to a predetermined threshold value, and an ONtime of the first switch is equal in each switch cycle, and an ON timeof the second switch is equal in each switch cycle.

According to still yet a further technical aspect of the presentinvention, a power source system is provided, including a PFC circuitand a control circuit. The PFC circuit includes: a first bridge arm anda second bridge arm. The first bridge arm includes a first switch and asecond switch connected with each other in series. A common node of thefirst switch and the second switch is coupled to one end of an inputvoltage through an inductor. The second bridge arm includes a thirdswitch and a fourth switch connected with each other in series. A commonnode of the third switch and the fourth switch is coupled to the otherend of the input voltage. The control circuit includes: a zero currentdetection circuit, a feedback circuit and a pulse distribution circuit.The zero current detection circuit has an edge detection circuit and anenabling circuit. The edge detection circuit is used to receive at leastone inductive signal reflecting the inductive voltage of the inductor,and detect and output a rising edge or a falling edge in the inductivesignal. The enabling circuit is used to filter the detected rising edgeor the detected falling edge so as to output a zero current detectionsignal. The feedback circuit is used to receive the zero currentdetection signal and a predetermined pulse signal and generate a drivingpulse signal. The pulse distribution circuit includes a polaritydetection circuit. The polarity detection circuit receives the inputvoltage and outputs a first digital signal and a second digital signalindicating a polarity of the input voltage. A potential of the firstdigital signal is opposite to that of the second digital signal. Thepulse distribution circuit distributes the received driving pulse signalto the first switch and the second switch of the first bridge armaccording to the first digital signal and the second digital signal sothat one of the first switch and the second switch performs an ONoperation. After a switch cycle, one of the first switch and the secondswitch performs the ON operation for the next switch cycle when thecurrent flowing through the inductor decreases to a predeterminedthreshold value, and an ON time of the first switch is equal in eachswitch cycle, and an ON time of the second switch is equal in eachswitch cycle.

According to a technical aspect of the present invention, a controlmethod used for a PFC circuit is provided. The PFC circuit includes aninductor, a first bridge arm and a second bridge arm connected to thefirst bridge arm in parallel. The first bridge arm has a first switchand a second switch connected with each other in series. A common nodeof the first switch and the second switch is coupled to an input voltagethrough the inductor. The control method includes the following steps:(a) receiving at least one inductive signal reflecting an inductivevoltage of the inductor and generating a zero current detection signalthrough an edge detection and filtering processing; (b) providing apredetermined pulse signal and generating a driving pulse signalaccording to the zero current detection signal and the predeterminedpulse signal; (c) detecting a polarity of the input voltage to output afirst digital signal and a second digital signal indicating the polarityof the input voltage; and (d) distributing the driving pulse signal tothe first switch and the second switch according to the first digitalsignal and the second digital signal so that one of the first switch andthe second switch performs an ON operation.

The current zero-crossing point detection is realized by using thecontrol circuit, control method and power source system used in thebridgeless PFC circuit of the present invention and through thecombination of the polarity detection of the input voltage and thevoltage detection of the auxiliary winding. Accordingly, the bridgelessPFC circuit is enabled to work in the critical conduction control mode,so that it is realized to turn on the switch in the first bridge armunder a zero voltage, thereby reducing the switch loss. Furthermore, thecombination of the driving pulse signal and the edge detection circuitis used to realize the zero-crossing detection of the inductor current,without detecting the phase/polarity of the input voltage. In this way,the bridgeless PFC circuit is also enabled to work in the criticalconduction control mode. The circuit design is simple and thezero-crossing detection of the inductor current is more reliable.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the foregoing as well as other aspects, features,advantages, and embodiments of the present invention more apparent, theaccompanying drawings are described as follows:

FIG. 1A illustrates a circuit structure diagram of a bridgeless PFCcircuit;

FIG. 1B illustrates a circuit structure diagram of a bridgeless PFCcircuit according to another one embodiment of the present disclosure;

FIG. 2 illustrates a schematic view of an inductor current waveform, apeak inductor current waveform, an average inductor current waveform anda driving signal waveform of the switch when the bridgeless PFC circuitin FIG. 1A works in the critical conduction mode (CRM);

FIG. 3( a) illustrates a schematic view of a current path when thesecond switch is on while the AC input voltage in FIG. 1 is a positivevoltage, and FIG. 3( b) illustrates a schematic view of a current pathwhen the second switch is off and the current is continued through thebody diode of the first switch while the AC input voltage in FIG. 1A isa positive voltage;

FIG. 3( c) illustrates a schematic view of a current path when the firstswitch is on while the AC input voltage in FIG. 1A is a negativevoltage, and FIG. 3(d) illustrates a schematic view of a current pathwhen the first switch is off and the current is continued through thebody diode of the second switch while the AC input voltage in FIG. 1A isa negative voltage;

FIG. 4 illustrates a structure diagram of a control circuit for a PFCcircuit according to an embodiment of the present invention;

FIG. 5 illustrates a first embodiment of the signal conversion circuitin the control circuit in FIG. 4;

FIG. 6 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the signal conversioncircuit in FIG. 5;

FIG. 7 illustrates a second embodiment of the signal conversion circuitin the control circuit in FIG. 4;

FIG. 8 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the signal conversioncircuit in FIG. 7;

FIG. 9 illustrates a third embodiment of the signal conversion circuitin the control circuit in FIG. 4;

FIG. 10 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the signal conversioncircuit in FIG. 9;

FIG. 11 illustrates a structure diagram of a control circuit for a PFCcircuit according to another embodiment of the present invention;

FIG. 12 illustrates a first embodiment of the edge detection circuit inthe control circuit in FIG. 11;

FIG. 13 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the edge detection circuitin FIG. 12;

FIG. 14 illustrates a second embodiment of the edge detection circuit inthe control circuit in FIG. 12;

FIG. 15 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the edge detection circuitin FIG. 14;

FIG. 16 illustrates a third embodiment of the edge detection circuit inthe control circuit in FIG. 12;

FIG. 17 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the edge detection circuitin FIG. 16;

FIG. 18 illustrates a fourth embodiment of the edge detection circuit inthe control circuit in FIG. 12; and

FIG. 19 illustrates a waveform schematic view of the currentzero-crossing detection signal outputted by the edge detection circuitin FIG. 18.

DETAILED DESCRIPTION

In order to make the description of the present invention more detailedand more comprehensive, various embodiments of the present invention aredescribed below with reference to the accompanying drawings. Whereverpossible, the same reference numbers are used in the drawings and thedescription to refer to the same or like parts. On the other hand,well-known elements and steps are not described in embodiments so as toavoid the unnecessary limitation to the present invention.

In the embodiments and claims, the description involving “electricalconnection” may generally mean that an element is indirectly connectedto another element through other electrical elements or an element isdirectly connected to another element without through other electricalelements.

In the embodiments and claims, the articles “a”, “an” and “the” refer toone or more, unless expressly specified otherwise.

As used herein, the terms “about”, “approximately”, “subsequently” or“near” are used to modify any micro-variable quantity, but thesemicro-variations do not change the nature of the quantity. In theembodiments the error of the quantity modified by terms “about”,“approximately”, “subsequently” or “near” is in a range of 20%,preferably in a range of 10%, and more preferably in a range of 5%,unless expressly specified otherwise.

FIG. 1A illustrates a circuit structure diagram of a bridgeless PFCcircuit. Referring to FIG. 1A, the bridgeless PFC (Power FactorCorrection) circuit includes a first bridge arm and a second bridge arm.The first bridge arm includes a first switch Q1 and a second switch Q2connected with each other in series (e.g., MOSFET). A common node of thefirst switch Q1 and the second switch Q2 is coupled to one end of aninput voltage through an inductor L1. The second bridge arm includes athird switch and a fourth switch connected with each other in series. Acommon node of the third switch and the fourth switch is coupled to theother end of the input voltage.

In an embodiment, each of the third switch and the fourth switch is aslow-recovery diode, as shown by D1 and D2 in FIG. 1A.

FIG. 1B illustrates a circuit structure diagram of a bridgeless PFCcircuit accroding to another one embodiment of the present disclosure.

In some other embodiments, as shown in FIG. 1B, each of the first switchQ1 and the second switch Q2 is a fast-recovery MOSFET. Each of the thirdswitch and the fourth switch is a slow-recovery MOSFET, as shown by Q3and Q4 in FIG. 1B. For example, the fast-recovery MOSFET is a wide bandgap semiconductor component, such as silicon carbide (SiC) or galliumnitride (GaN).

FIG. 2 illustrates a schematic view of an inductor current waveform, apeak inductor current waveform, an average inductor current waveform anda driving signal waveform of the switch when the bridgeless PFC circuitin FIG. 1A works in the critical conduction mode (CRM).

Referring to FIG. 2, when the bridgeless PFC circuit works in the CR theend of each switch cycle (or at the start of the next switch cycle), theinductor current just decreases to zero. It can be known from the figurethat when one of the switches Q1 and Q2 in the first bridge arm receivesa driving signal, from the ON time of the switch, the inductor currentgradually increases and reaches the peak current (the period correspondsto the ON time). Thereafter, the switch is off and the inductor currentgradually decreases from the peak current to zero (the periodcorresponds to the OFF time). Since each switch cycle includes therising period and the falling period of the inductor current, the commonpoint of the rising period and the falling period is connected (i.e. apoint corresponding to the peak current) to form the peak current curvein FIG. 2. Additionally, according to the inductor current curve and thepeak current curve, the corresponding average current curve also can beobtained.

FIG. 3( a) illustrates a schematic view of a current path when thesecond switch is on while the AC input voltage in FIG. 1A is a positivevoltage. FIG. 3( b) illustrates a schematic view of a current path whenthe second switch is off and the current is continued through the bodydiode of the first switch while the AC input voltage in FIG. 1A is apositive voltage.

Referring to FIGS. 3( a) and 3(b), in view of the condition that theinput voltage is a positive voltage, if the switch Q2 is on and theswitch Q1 is off, the current path is formed by the inductor L, theswitch Q2 and the diode D2. If the switch Q1 and the switch Q2 are bothoff, the current path is formed by the inductor L, the body diode of theswitch Q1, the capacitor and the diode D2.

FIG. 3( c) illustrates a schematic view of a current path when the firstswitch is on while the AC input voltage in FIG. 1A is a negativevoltage. FIG. 3( d) illustrates a schematic view of a current path whenthe first switch is off and the current is continued through the bodydiode of the second switch while the AC input voltage in FIG. 1A is anegative voltage.

Referring to FIGS. 3( c) and 3(d), in view of the condition that theinput voltage is a negative voltage, if the switch Q1 is on and theswitch Q2 is off, the current path is formed by the inductor L, theswitch Q1 and the diode D1 If the switch Q1 and the switch Q2 are bothoff, the current path is formed by the inductor L, the body diode of theswitch Q2, the capacitor and the diode D1.

FIG. 4 illustrates a structure diagram of a control circuit for a PFCcircuit according to an embodiment of the present invention.

Referring to FIG. 4, the control circuit for the bridgeless PFC circuitincludes a zero current detection circuit, a feedback circuit and apulse distribution circuit.

The zero current detection circuit includes a polarity detection circuitand a signal conversion circuit. The polarity detection circuit receivesthe input voltage of the AC power source and outputs a first digitalsignal and a second digital signal indicating the polarity of the inputvoltage. Herein, the potential polarity of the first digital signal isalways opposite to that of the second digital signal. When the firstdigital signal is at a high potential, the second digital signal is at alow potential. When the first digital signal is at a low potential, thesecond digital signal is at a high potential. The signal conversioncircuit receives at least one inductive signal reflecting the inductivevoltage of the inductor L1, the above-mentioned first digital signal andsecond digital signal and generates an analog signal.

It should be understood that the control circuit can output an inductivesignal reflecting the inductive voltage of the inductor through twoauxiliary windings or through a single auxiliary winding. For example,one of two auxiliary windings is used to output the inductive signalwhen the polarity of the voltage is positive. The other auxiliarywinding is used to output the inductive signal when the polarity of thevoltage is negative. Also for example, one end of a single auxiliarywinding is used to output the inductive signal when the polarity of thevoltage is positive. The other end of the single auxiliary winding isused to output the inductive signal when the polarity of the voltage isnegative.

The feedback circuit is used to receive the analog signal from thesignal conversion circuit and a predetermined pulse signal and generatea driving pulse signal according to the analog signal and thepredetermined pulse signal. The pulse distribution circuit iselectrically coupled to the polarity detection circuit and the feedbackcircuit. The pulse distribution circuit is used to distribute thedriving pulse signal outputted by the feedback circuit to the firstswitch Q1 and the second switch Q2 of the first bridge arm according tothe first digital signal and the second digital signal from the polaritydetection circuit. Accordingly, one of the first switch Q1 and thesecond switch Q2 performs an ON operation. After a switch cycle, one ofthe first switch Q1 and the second switch Q2 performs the ON operationfor the next switch cycle when the current flowing through the inductorL1 decreases to a predetermined threshold value, and an ON time of thefirst switch Q1 is equal in each switch cycle and an ON time of thesecond switch Q2 is equal in each switch cycle.

In an embodiment, the polarity detection circuit includes a firstoperational amplifier 100, a first comparator 102 and a first inverter104.

The first operational amplifier 100 has a first input end (such as apositive-phase input end), a second input end (such as a negative-phaseinput end) and an output end. The first input end and the second inputend of the first operational amplifier 100 are connected to two ends ofthe input voltage respectively. The output end of the first operationalamplifier 100 is used to output a voltage signal reflecting the polarityof the input voltage. The first comparator 102 has a first input end, asecond input end and an output end. The first input end of the firstcomparator 102 is coupled to the output end of the first operationalamplifier 100. The second input end of the first comparator 102 iscoupled to a first reference voltage (such as a ground voltage). Theoutput end of the first comparator 102 is used to output the firstdigital signal. The first inverter 104 is used to convert the firstdigital signal into a second digital signal. Therefore, the polaritydetection circuit outputs the first digital signal and the seconddigital signal. The potential polarity of the first digital signal isalways opposite to that of the second digital signal.

In an embodiment, the feedback circuit includes a second operationalamplifier 200, a second comparator 202 and a RS trigger 204.

The second operational amplifier 200 has a first input end (such as anegative-phase input end), a second input end (such as a positive-phaseinput end) and an output end. The first input end of the secondoperational amplifier 200 is used to receive the output voltage of thepower factor control circuit (i.e., a load voltage across two ends of acapacitor). The second input end of the second operational amplifier 200is coupled to a second reference voltage (such as V_(ref)). The outputend of the second operational amplifier 200 outputs a differenceamplification signal. The second comparator 202 has a first input end, asecond input end and an output end. The first input end of the secondcomparator 202 is coupled to the output end of the second operationalamplifier 200. The second input end of the second comparator 202 is usedto receive a saw-tooth wave voltage signal. The output end of the secondcomparator 202 outputs the predetermined pulse signal. The RS trigger204 has a preset end S, a reset end R and an output end Q. The presetend S of the RS trigger 204 is used to receive the analog signal V_(ZCD)from the signal conversion circuit. The reset end R of the RS trigger204 is used to receive the predetermined pulse signal from the secondcomparator 202. The output end of the RS trigger 204 is used to outputthe driving pulse signal.

Additionally, the feedback circuit further includes a delay circuit 206arranged between the signal conversion circuit and the RS trigger 204.The delay circuit 206 is used to delay the analog signal V_(ZCD) andsend the delayed analog signal to the preset end S of the RS trigger204. Furthermore, the feedback circuit further includes a comparing unit(not shown) arranged between the delay circuit 206 and the RS trigger204. The comparing unit is used to convert the delayed analog signalinto a corresponding digital delay signal and send it to the preset endS of the RS trigger 204.

In an embodiment, the pulse distribution circuit includes a first ANDgate circuit 300 and a second AND gate circuit 302.

The first AND gate circuit 300 has a first input end, a second input endand an output end. The first input end of the first AND gate circuit 300is used to receive the first digital signal from the polarity detectioncircuit. The second input end of the first AND gate circuit 300 is usedto receive the driving pulse signal from the feedback circuit. Theoutput end of the first AND gate circuit 300 outputs a first controlsignal to the first switch Q1 of the first bridge arm.

The second AND gate circuit 302 has a first input end, a second inputend and an output end. The first input end of the second AND gatecircuit 302 is used to receive the second digital signal from thepolarity detection circuit. The second input end of the second AND gatecircuit 302 is used to receive the driving pulse signal from thefeedback circuit. The output end of the second AND gate circuit 302outputs a second control signal to the second switch Q2 of the firstbridge arm. Since the driving pulse signal received by the second ANDgate circuit 302 is the same as the driving pulse signal received by thefirst AND gate circuit 300 and the potential polarity of the seconddigital signal is always opposite to that of the first digital signal,only one of the first switch Q1 and the second switch Q2 in the firstbridge arm is on and the other switch is off at any moment.

For example, when the polarity of the input voltage is positive, thefirst digital signal is at a low potential and the second digital signalis at a high potential. When the polarity of the input voltage isnegative, the first digital signal is at a high potential and the seconddigital signal is at a low potential.

Those of skills in the art should understand that FIG. 4 not only can beused to describe the control circuit for the bridgeless PFC circuit butalso can be used to describe the power source system including thebridgeless PFC circuit and the control circuit and the control methodcorresponding to the control circuit.

Taking a control method for the bridgeless PFC circuit as an example, inthis control method, firstly the polarity of the input voltage isdetected so as to output a first digital signal and a second digitalsignal indicating the polarity of the input voltage; subsequently ananalog signal V_(ZCD) is generated through the signal conversionprocessing according to at least one inductive signal reflecting theinductive voltage of the inductor, the first digital signal and thesecond digital signal; thereafter a predetermined pulse signal isprovided and a driving pulse signal is generated according to the analogV_(ZCD) and the predetermined pulse signal; and finally the drivingpulse signal is distributed to the first switch Q1 and the second switchQ2 according to the first digital signal and the second digital signal,so that one of the first switch Q1 and the second switch Q2 performs theON operation.

FIG. 5 illustrates a first embodiment of the signal conversion circuitin the control circuit in FIG. 4. FIG. 6 illustrates a waveformschematic view of the current zero-crossing detection signal outputtedby the signal conversion circuit in FIG. 5.

Referring to FIG. 5, the control circuit includes a first auxiliarywinding AUX1 and a second auxiliary winding AUX2 which are both coupledto the inductor L1. A polarity of a first inductive signal generated bythe first auxiliary winding AUX1 is opposite to that of a secondinductive signal generated by the second auxiliary winding AUX2.

In an embodiment, the signal conversion circuit includes a first analogswitch and a second analog switch. The first analog switch is formed bya first resistor R1, a third diode D3 and a first switch MOS1. Thesecond analog switch is formed by a second resistor R2, a fourth diodeD4 and a second switch MOS2.

One end of the first resistor R1 is connected to the first end of thefirst auxiliary winding AUX1. The anode of the third diode D3 isconnected to the other end of the first resistor R1. The cathode of thethird diode D3 is connected to the output end of the signal conversioncircuit so as to output the analog signal V_(ZCD). The first end of thefirst switch MOS1 is connected to the other end of the first resistor R1and the anode of the third diode D3. The second end of the first switchMOS1 is connected to the ground end. The control end of the first switchMOS1 is used to receive the second digital signal V_(pos).

One end of the second resistor R2 is connected to the first end of thesecond auxiliary winding AUX2. The second ends of the second auxiliarywinding AUX2 and the first auxiliary winding AUX1 are connected to theground end respectively. The anode of the fourth diode D4 is connectedto the other end of the second resistor R2. The cathode of the fourthdiode D4 is connected to the output end of the signal conversion circuitso as to output the analog signal V_(ZCD). The first end of the secondswitch. MOS2 is connected to the other end of the second resistor R2 andthe anode of the fourth diode D4. The second end of the second switchMOS2 is connected to the ground end. The control end of the secondswitch MOS2 is used to receive the first digital signal V_(neg).

It can be known from FIG. 6 that in an input voltage cycle, the waveformof the voltage V_(AUX1) across two ends of the first auxiliary windingis always opposite to that of the voltage V_(AUX2) across two ends ofthe second auxiliary winding. Furthermore, the waveform of the potentialV_(a) at the common node of the resistor R1 and the diode D3 in thefirst analog switch is just opposite to that of the potential V_(b) atthe common node of the resistor R2 and the diode D4 in the second analogswitch in the first half cycle and the second half cycle of the inputvoltage. For example, in the first half cycle of the input voltage, thepotential V_(a) is a low potential and the potential V_(b) varies alongwith the voltage waveform of the second auxiliary winding.Correspondingly, the waveform of the analog signal V_(ZCD) outputted bythe signal conversion circuit is the same as that of the potentialV_(b). Also for example, in the second half cycle of the input voltage,the potential V_(b) is a low potential and the potential V_(a) variesalong with the voltage waveform of the first auxiliary winding.Correspondingly, the waveform of the analog signal V_(ZCD) outputted bythe signal conversion circuit is the same as that of the potentialV_(a).

Additionally, in the waveform of the analog signal V_(ZCD), the periodfrom t1 to t2 represents a stage that the inductor current decreasesfrom the positive peak to zero. The period from t2 to t3 represents astage that the inductor current varies from zero to the negative peak.The period from t3 to t4 represents a stage that the inductor currentrecovers from the negative peak to the zero current. Similarly, theperiod from t5 to t6 represents a stage that the inductor current variesfrom the negative peak to the zero current. The period from t6 to t7represents a stage that the inductor current varies from zero to thepositive peak. The period from t7 to t8 represents a stage that theinductor current decreases from the positive peak to zero.

FIG. 7 illustrates a second embodiment of the signal conversion circuitin the control circuit in FIG. 4. FIG. 8 illustrates a waveformschematic view of the current zero-crossing detection signal outputtedby the signal conversion circuit in FIG. 7.

Referring to FIG. 7, the control circuit includes a first auxiliarywinding AUX1 and a second auxiliary winding AUX2 which are both coupledto the inductor L1. A polarity of a first inductive signal generated bythe first auxiliary winding AUX1 is opposite to that of a secondinductive signal generated by the second auxiliary winding AUX2.

In an embodiment, the signal conversion circuit includes a first analogswitch and a second analog switch. The first analog switch is formed bya fifth resistor R5, a third switch MOS3 and a fifth switch MOS5. Thesecond analog switch is formed by a sixth resistor RS, a fourth switchMOS4 and a sixth switch MOS6.

One end of the fifth resistor R5 is connected to the first end of thefirst auxiliary winding AUX1. The first end of the third switch MOS3 isconnected to the first end of the first auxiliary winding AUX1. Thesecond end of the third switch MOS3 is connected to the anode of aseventh diode D7. The control end of the third switch MOS3 is connectedto the other end of the fifth resistor R5. The first end of the fifthswitch MOS5 is connected to the other end of the fifth resistor R5 andthe control end of the third switch MOS3. The second end of the fifthswitch MOS5 is connected to the ground end. The control end of the fifthswitch MOS5 is used to receive the first digital signal V_(neg).

One end of the sixth resistor R6 is connected to the first end of thesecond auxiliary winding AUX2. The second ends of the second auxiliarywinding AUX2 and the first auxiliary winding AUX1 are connected to theground end respectively. The first end of the fourth switch MOS4 isconnected to the first end of the second auxiliary winding AUX2. Thesecond end of the fourth switch MOS4 is connected to the anode of aneighth diode D8. The control end of the fourth switch MOS4 is connectedto the other end of the sixth resistor R6. The first end of the sixthswitch MOS6 is connected to the other end of the sixth resistor R6 andthe control end of the fourth switch MOS4. The second end of the sixthswitch MOS6 is connected to the ground end. The control end of the sixthswitch MOS6 is used to receive the second digital signal V_(pos). Thecathodes of the seventh diode D7 and the eighth diode D8 are connectedto the output end of the signal conversion circuit respectively so as tooutput the analog signal V_(ZCD).

The respective waveforms of the first auxiliary winding AUX1, the secondauxiliary winding AUX2 and the analog signal V_(ZCD) in FIG. 8 are thesame as or similar to FIG. 6, and it is not illustrated any more forpurpose of convenience.

FIG. 9 illustrates a third embodiment of the signal conversion circuitin the control circuit in FIG. 4. FIG. 10 illustrates a waveformschematic view of the current zero-crossing detection signal outputtedby the signal conversion circuit in FIG. 9.

Referring to FIG. 9, the control circuit includes the single auxiliarywinding AUX1 coupled to the inductor L1. The analog signal V_(ZCD) isgenerated by a third inductive signal generated by the auxiliary windingAUX1, the first digital signal and the second digital signal.

In an embodiment, the signal conversion circuit includes a first analogswitch and a second analog switch. The first analog switch is formed bya seventh resistor R7, a ninth diode D9 and a seventh switch MOS7. Thesecond analog switch is formed by an eighth resistor R8, a tenth diodeD10 and an eighth switch MOS8.

One end of the seventh resistor R7 is connected to the first end of theauxiliary winding AUX1. The anode of the ninth diode D9 is connected tothe other end of the seventh resistor R7. The cathode of the ninth diodeD9 is connected to the output end of the signal conversion circuit so asto output the analog signal V_(ZCD). The first end of the seventh switchMOS7 is connected to the other end of the seventh resistor R7 and theanode of the ninth diode D9. The second end of the seventh switch MOS7is connected to the ground end. The control end of the seventh switchMOS7 is used to receive the second digital signal V_(pos).

One end of the eighth resistor R8 is connected to the second end of theauxiliary winding AUX1. The anode of the tenth diode D10 is connected tothe other end of the eighth resistor R8. The cathode of the tenth diodeD10 is connected to the output end of the signal conversion circuit soas to output the analog signal V_(ZCD). The first end of the eighthswitch MOS8 is connected to the other end of the eighth resistor R8 andthe anode of the tenth diode D10. The second end of the eighth switchMOS8 is connected to the ground end. The control end of the eighthswitch MOS8 is used to receive the first digital signal V_(neg).

Referring to FIGS. 9 and 10, in the first half cycle of the inputvoltage, the first digital signal V_(neg) is at a low potential and thesecond digital signal V_(pos) is at a high potential. At this time theseventh switch MOS7 is on and the eighth switch MOS8 is off. Therefore,the potential of V_(a3) is maintained as the ground voltage, and at thistime the potential of V_(b3) varies along with the voltage waveform ofthe negative terminal of the auxiliary winding AUX1 (opposite to thevariation trend of voltage waveform V_(AUX1) of the auxiliary winding).Similarly, in the second half cycle of the input voltage, the firstdigital signal V_(neg) is at a high potential and the second digitalsignal V_(pos) is at a low potential. At this time the seventh switchMOS7 is of and the eighth witch MOS8 is on. Therefore, the potential ofV_(b3) is maintained as the ground voltage, and at this time thepotential of V_(a3) varies along with the voltage waveform of thepositive terminal of the auxiliary winding AUX1 (the same as thevariation trend of voltage waveform V_(AUX1) of the auxiliary winding).

FIG. 11 illustrates a structure diagram of a control circuit for a PFCcircuit according to another embodiment of the present invention.

Referring to FIG. 11, the control circuit for the bridgeless PFC circuitincludes a zero current detection circuit, a feedback circuit and apulse distribution circuit.

The zero current detection circuit includes an edge detection circuit406 and an enabling circuit. The edge detection circuit 406 receives atleast one inductive signal reflecting the inductive voltage of theinductor L1 and detects and outputs the rising edge or the falling edgein the inductive signal. The enabling circuit filters the detectedrising edge or the detected falling edge and outputs a zero currentdetection signal V_(ZCD).

The feedback circuit is used to receive the zero current detectionsignal V_(ZCD) and a predetermined pulse signal and generates a drivingpulse signal according to the analog signal and the predetermined pulsesignal. The pulse distribution circuit includes a polarity detectioncircuit. The polarity detection circuit receives the input voltage andoutputs a first digital signal and a second digital signal indicatingthe polarity of the input voltage. The potential of the first digitalsignal is opposite to that of the second digital signal. The pulsedistribution circuit distributes the received driving pulse signal tothe first switch Q1 and the second switch Q2 of the first bridge armaccording to the first digital signal and the second digital signal sothat one of the first switch Q1 and the second switch Q2 performs the ONoperation. After a switch cycle, one of the first switch Q1 and thesecond switch Q2 performs the ON operation for the next switch cyclewhen the current flowing through the inductor L1 decreases to apredetermined threshold value, and an ON time of the first switch Q1 isequal in each switch cycle and an ON time of the second switch Q2 isequal in each switch cycle.

Comparing FIG. 11 with FIG. 4, the main difference is that the polaritydetection circuit in FIG. 11 does not detect the zero-crossing point ofthe inductor current waveform any longer and is instead used todistribute the driving pulse signal to the switch Q1 or the switch Q.That is, the first digital signal and the second digital signaloutputted by the polarity detection circuit in FIG. 11, indicating thepolarity of the input voltage, act on the driving pulse signal so as tocontrol the ON operation of switch Q1 or the switch Q2. By comparison,the polarity detection circuit in FIG. 4 needs to send the first digitalsignal and the second digital signal into the signal conversion circuitso that the signal conversion circuit makes use of the first digitalsignal, the second digital signal and the inductive signal to output theanalog signal V_(ZCD), i.e., the analog signal for the zero currentdetection (ZCD).

In an embodiment, the polarity detection circuit includes a firstoperational amplifier 604, a first comparator 606 and a first inverter608. The first operational amplifier 604, the first comparator 606 andthe first inverter 608 have the same or similar connection manner withthe first operational amplifier 100, the first comparator 102 and thefirst inverter 104 in FIG. 4, and thus it is not illustrated any morefor purpose of convenience.

In another embodiment, the feedback circuit includes a secondoperational amplifier 500, a second comparator 502 and a RS trigger 504The second operational amplifier 500, the second comparator 502 and theRS trigger 504 have the same or similar connection manner with thesecond operational amplifier 200, the second comparator 202 and the RStrigger 204 in FIG. 4, and thus it is not illustrated any more forpurpose of convenience.

Additionally, the zero current detection circuit further includes adelay circuit 408 arranged between the enabling circuit and the RStrigger 504. The delay circuit 408 is used to delay the zero currentdetection signal V_(ZCD) and send the delayed zero current detectionsignal to the preset end S of the RS trigger 504. As shown in FIG. 11,the enabling circuit is formed by the switch MOS1, the resistor R1 andthe capacitor C2. The enabling circuit is used to select a correct edgesignal and avoid generating a wrong current zero-crossing detectionsignal. Further details are described below with reference to FIGS. 12and 13.

In an embodiment, the zero current detection circuit further includes acomparing unit (not shown) arranged between the delay circuit 408 andthe RS trigger 504. The comparing unit is used to convert the delayedzero current detection signal into a corresponding digital delay signaland send it to the preset end S of the RS trigger 504.

In another embodiment, the pulse distribution circuit includes a firstAND gate circuit 600 and a second AND gate circuit 602.

The first AND gate circuit 600 has a first input end, a second input endand an output end. The first input end of the first AND gate circuit 600is used to receive the first digital signal from the polarity detectioncircuit. The second input end of the first AND gate circuit 600 is usedto receive the driving pulse signal from the feedback circuit. Theoutput end of the first AND gate circuit 600 outputs a first controlsignal to the first switch Q1 of the first bridge arm.

The second AND gate circuit 602 has a first input end, a second inputend and an output end. The first input end of the second AND gatecircuit 602 is used to receive the second digital signal from thepolarity detection circuit. The second input end of the second AND gatecircuit 602 is used to receive the driving pulse signal from thefeedback circuit. The output end of the second AND gate circuit 602outputs a second control signal to the second switch. Q2 of the firstbridge arm. Since the driving pulse signal received by the second ANDgate circuit 602 is the same as the driving pulse signal received by thefirst AND gate circuit 600 and the potential polarity of the seconddigital signal is always opposite to that of the first digital signal,only one of the first switch Q1 and the second switch Q2 in the firstbridge arm is on and the other switch is off at any moment.

For example, when the polarity of the input voltage is positive, thefirst digital signal is at a low potential and the second digital signalis at a high potential. When the polarity of the input voltage isnegative, the first digital signal is at a high potential and the seconddigital signal is at a low potential.

In an embodiment, the enabling circuit includes the switch MOS1, theresistor R1 and the capacitor C2. In particular, the first end of theswitch MOS1 is electrically connected to the first end of the resistorR1. The second end of the switch MOS1 is connected to the output end ofthe edge detection circuit 406. The third end of the switch MOS1 isconnected to the ground voltage. The first end of the resistor RI iselectrically connected to the first end of the switch MOS1. The secondend of the resistor R1 is electrically connected to the output end ofthe feedback circuit. One end of the capacitor C2 is connected to thefirst end of the switch MOS1 and the first end of the resistor R1. Theother end of the capacitor C2 is connected to the third end of theswitch MOS1. The enabling circuit filters the rising edge or the fallingedge in the inductive signal outputted by the edge detection circuit 406according to the driving pulse signal outputted by the feedback circuitso as to extract a correct edge signal.

Those of skills in the art should understand that FIG. 11 not only canbe used to describe the control circuit for the bridgeless PFC circuitbut also can be used to describe the power source system including thebridgeless PFC circuit and the control circuit and the control methodcorresponding to the control circuit.

Taking a control method for the bridgeless PFC circuit as an example, inthis control method, firstly at least one inductive signal reflectingthe inductive voltage of the inductor is received and a zero currentdetection signal generated through the edge detection and filteringprocessing; subsequently a predetermined pulse signal is provided and adriving pulse signal is generated according to the zero currentdetection signal and the predetermined pulse signal; thereafter thepolarity of the input voltage is detected to output a first digitalsignal and a second digital signal indicating the polarity of the inputvoltage; and finally the driving pulse signal is distributed to thefirst switch Q1 and the second switch Q2 according to the first digitalsignal and the second digital signal, so that one of the first switch Q1and the second switch Q2 performs the ON operation.

FIG. 12 illustrates a first embodiment of the edge detection circuit inthe control circuit in FIG. 11. FIG. 13 illustrates a waveform schematicview of the current zero-crossing detection signal outputted by the edgedetection circuit in FIG. 12.

Referring to FIG. 12, the control circuit includes a first auxiliarywinding AUX1 and a second auxiliary winding AUX2 which are both coupledto the inductor L1. The polarity of a first inductive signal generatedby the first auxiliary winding AUX1 is opposite to that of a secondinductive signal generated by the second auxiliary winding AUX2.

In an embodiment, the edge detection circuit includes a first analogswitch and a second analog switch. The first analog switch is formed bya third resistor R3, a fifth diode D5 and a third capacitor C3. Thesecond analog switch is formed by a fourth resistor R4, a sixth diode D6and a fourth capacitor C4.

One end of the third resistor R3 is connected to the first end of thefirst auxiliary winding AUX1 The cathode of the fifth diode D5 isconnected to the first end of the first auxiliary winding AUX1. Theanode of the fifth diode D5 is connected to the other end of the thirdresistor R3. One end of the third capacitor C3 is connected to the anodeof the fifth diode D5. The other end of the third capacitor C3 isconnected to the ground end.

One end of the fourth resistor R4 is connected to the first end of thesecond auxiliary winding AUX2. The second ends of the second auxiliarywinding AUX2 and the first auxiliary winding AUX1 are connected to theground end respectively. The cathode of the sixth diode D6 is connectedto the first end of the second auxiliary winding AUX2. The anode of thesixth diode D6 is connected to the other end of the fourth resistor R4.One end of the fourth capacitor C4 is connected to the anode of thesixth diode D6. The other end of the fourth capacitor C4 is connected tothe ground end. The anode of the fifth diode D5 and the anode of thesixth diode D6 are connected to the third diode D3 and the fourth diodeD4 respectively, so as to output the zero current detection signalV_(ZCD) through the third diode D3 and the fourth diode D4.

Referring to FIGS. 12 and 13, at t1, the voltage V_(c3) on the capacitorC3 is changed from a positive voltage signal to a negative voltagesignal with one falling edge. If the above-mentioned enabling circuit isnot provided, after the logic AND circuit formed by the diode D3 and thediode D4, V_(ZCD) generates a corresponding falling edge waveform at thesame time as t1. However, the falling edge is caused by the reversion ofthe voltage across two ends of the auxiliary winding due to the actionof the switch, which is not a correct edge signal. Therefore, thedriving signal V_(DRV) of the switch is received by the enablingcircuit. A certain delay is generated according to the resistor R1 andthe capacitor C2 in order to drive the switch MOS1, so that V_(ZCD) s asignal at a low potential during the period when V_(DRV) is positive,such as V_(TH) in FIG. 13. In this way, a wrong hopping signal isfiltered through V_(ZCD) and the enabling circuit and a correct zerocurrent detection signal is obtained.

FIG. 14 illustrates a second embodiment of the edge detection circuit inthe control circuit in FIG. 12. FIG. 15 illustrates a waveform schematicview of the current zero-crossing detection signal outputted by the edgedetection circuit in FIG. 14.

Referring to FIG. 14, the edge detection circuit includes a firstdetection module and a second detection module. The first detectionmodule is formed by a first operational amplifier A2-1, a RC circuit, aninverter N2-1 and a NAND gate circuit 2-1. The second detection moduleis formed by a second operational amplifier A2-2, a RC circuit, aninverter N2-2 and a NAND gate circuit 2-2.

The first operational amplifier A2-1 has a first input end, a secondinput end and an output end. The first input end of the firstoperational amplifier A2-1 is connected to the first end of the firstauxiliary winding AUX1. The second input end of the first operationalamplifier A2-1 is connected to a ground voltage. The output end of thefirst operational amplifier A2-1 outputs a first digital signalV_(D2-1). The RC circuit has a first resistor R2-1 and a first capacitorC2-1. One end of the first resistor R2-1 is connected to the output endof the first operational amplifier A2-1. One end of the first capacitorC2-1 is connected to the ground end. The input end of the inverter N2-1is connected to the common node of the first resistor R2-1 and the firstcapacitor C2-1. The NAND gate circuit 2-1 has a first input end, asecond input end and an output end. The first input end of the NAND gatecircuit 2-1 is connected to the output end of the first operationalamplifier A2-1. The second input end of the NAND gate circuit 2-1 isconnected to the output end of the inverter N2-1. The output end of theNAND gate circuit 2-1 outputs a first pulse signal V_(D2-3).

The second operational amplifier A2-2 has a first input end, a secondinput end and an output end. The first input end of the secondoperational amplifier A2-2 is connected to the first end of the secondauxiliary winding AUX2. The second input end of the second operationalamplifier A2-2 is connected to a ground voltage. The output end of thesecond operational amplifier A2-2 outputs a second digital signalV_(D2-2). The RC circuit has a second resistor R2-2 and a secondcapacitor C2-2 One end of the second resistor R2-2 is connected to theoutput end of the second operational amplifier A2-2. One end of thesecond capacitor C2-2 is connected to the ground end. The input end ofthe inverter N2-2 is connected to the common node of the second resistorR2-2 and the second capacitor C2-2. The NAND gate circuit 2-2 has afirst input end, a second input end and an output end. The first inputend of the NAND gate circuit 2-2 is connected to the output end of thesecond operational amplifier A2-2. The second input end of the NAND gatecircuit 2-2 is connected to the output end of the inverter N2-2. Theoutput end of the NAND gate circuit 2-2 outputs a second pulse signalV_(D2-4). The logic AND operation is performed for the first pulsesignal V_(D2-3) and the second pulse signal V_(D2-4) to obtain the zerocurrent detection signal.

Referring to FIG. 15, the first digital signal V_(D2-1) outputted by thefirst operational amplifier A2-1 is used to detect the rising edge ofthe voltage waveform of the auxiliary winding AUX1. The second digitalsignal V_(D2-2) outputted by the second operational amplifier A2-2 isused to detect the rising edge of the voltage waveform of the auxiliarywinding AUX2. Therefore, the edge detection circuit is also referred toas the rising edge detection circuit. Additionally, the zero currentdetection signal V_(ZCD2) is the voltage waveform obtained when thelogic AND operation is performed for the first pulse signal V_(D2-3) andthe second pulse signal V_(D2-4).

FIG. 16 illustrates a third embodiment of the edge detection circuit inthe control circuit in FIG. 12. FIG. 17 illustrates a waveform schematicview of the current zero-crossing detection signal outputted by the edgedetection circuit in FIG. 16.

Referring to FIG. 16 the control circuit includes the single auxiliarywinding AUX1 coupled to the inductor L1. A third inductive signalgenerated by the auxiliary winding AUX1 is used to detect and output therising edge or the falling edge in the third inductive signal.

The edge detection circuit includes a detection module. The detectionmodule has an operational amplifier A3-1, a RC circuit, an inverterN3-1, a NAND gate circuit 3-1 and an OR gate circuit 3-2.

The operational amplifier A3-1 has a first input end, a second input endand an output end. The first input end of the operational amplifier A3-1is connected to the first end of the auxiliary winding AUX1. The secondinput end of the operational amplifier A3-1 is connected to a groundend. The output end of the operational amplifier A3-1 outputs a digitalsignal V_(D3-1). The RC circuit has a resistor R3-1 and a capacitorC3-1. One end of the resistor R3-1 is connected to the output end of theoperational amplifier A3-1. One end of the capacitor C3-1 is connectedto the ground end. The input end of the inverter N3-1 is connected tothe common node of the resistor R3-1 and the capacitor C3-1. The NANDgate circuit 3-1 has a first input end, a second input end and an outputend. The first input end of the NAND gate circuit 3-1 is connected tothe output end of the operational amplifier A3-1. The second input endof the NAND gate circuit 3-1 is connected to the output end of theinverter N3-1. The output end of the NAND gate circuit 3-1 outputs afirst pulse signal V_(D3-3). The OR gate circuit 3-2 has a first inputend, a second input end and an output end. The first input end of the ORgate circuit 3-2 is connected to the output end of the operationalamplifier A3-1. The second input end of the OR gate circuit 3-2 isconnected to the output end of the inverter N3-1. The output end of theOR gate circuit 3-2 outputs a second pulse signal V_(D3-4). The logicAND operation is performed for the first pulse signal V_(D3-3) and thesecond pulse signal V_(D3-4) to obtain the zero current detection signalV_(ZCD3).

Referring to FIGS. 16 and 17, the rising edge detection circuit isformed by the resistor R3-1, the capacitor C3-1, the NOT gate N3-1 andthe NAND gate 3-1, so as to convert the rising edge of the inductivevoltage of the auxiliary winding AUX1 into the negative-logic narrowpulse V_(D3-3). The falling edge detection circuit is formed by theresistor R3-1, the capacitor C3-1, the NOT gate N3-1 and the OR gate3-2, so as to convert the falling edge of the inductive voltage of theauxiliary winding AUX1 into the negative-logic narrow pulse V_(D3-4).The AND gate 3-3 combines the narrow pulses respectively formed by therising edge detection circuit and the falling edge detection circuit soas to generate the zero current detection signal V_(ZCD3). Therefore, inthe embodiment, both the rising edge and the falling edge of theinductive voltage waveform of the auxiliary winding can be convertedinto the negative-logic narrow pulse so as to realize the functions ofthe rising edge detection and falling edge detection.

FIG. 18 illustrates a fourth embodiment of the edge detection circuit inthe control circuit in FIG. 12. FIG. 19 illustrates a waveform schematicview of the current zero-crossing detection signal outputted by the edgedetection circuit in FIG. 18.

Referring to FIG. 18, the control circuit includes the single auxiliarywinding AUX1 coupled to the inductor L1. An inductive signal generatedby the auxiliary winding AUX1 is used to detect and output the risingedge or the falling edge in the inductive signal.

The edge detection circuit includes a first optical coupler 4-1 and asecond optical coupler 4-2. The first input end of the first opticalcoupler 4-1 is connected to the second end of the auxiliary windingAUX1. The second input end of the first optical coupler 4-1 is connectedto the first end of the auxiliary winding AUX1 through a first resistorR4-1. The first output end of the first optical coupler 4-1 is connectedto a power source voltage V_(CC). The first input end of the secondoptical coupler 4-2 is connected to the second input end of the firstoptical coupler 4-1. The second input end of the second optical coupler4-2 is connected to the second end of the auxiliary winding AUX1. Thefirst output end of the second optical coupler 4-2 is connected to thepower source voltage V_(CC). The second output end of the second opticalcoupler 4-2 is connected to the second output end of the first opticalcoupler 4-1 so as to output the zero current detection signal V_(ZCD4).

Referring to FIGS. 18 and 19, when the inductive voltage of theauxiliary winding AUX1 has no hop, the inductive voltage can make one ofthe optical coupler 4-1 and the optical coupler 4-2 on so that the zerocurrent detection signal V_(ZCD4) is at a high potential. When theinductive voltage of the auxiliary winding is reversed (includingconditions that the inductive voltage is modulated from the negativevoltage to the positive voltage and from the positive voltage to thenegative voltage), it is sure that the inductive voltage passes thecommon cutoff region of the optical coupler 4-1 and the optical coupler4-2. At this time, the zero current detection signal V_(ZCD4) is at alow potential so as to output a negative-logic narrow pulse. In thisway, the edge detection function for the inductive voltage of theauxiliary winding also can be realized so that the zero-crossing pointof the inductor current can be determined.

Although the present invention has been disclosed with reference to theabove embodiments, these embodiments are not intended to limit thepresent invention. It will be apparent to those of skills in the artthat various modifications and variations can he made without departingfrom the spirit and scope of the present invention. Therefore, the scopeof the present invention shall be defined by the appended claims.

What is claimed is:
 1. A control circuit for a PFC circuit, wherein thePFC circuit comprises an inductor, a first bridge arm and a secondbridge arm connected to the first bridge arm in parallel, the firstbridge arm has a first switch and a second switch connected with eachother in series, and a common node of the first switch and the secondswitch is coupled to an input voltage through the inductor, the controlcircuit comprising: a zero current detection circuit, comprising: apolarity detection circuit, for receiving the input voltage andoutputting a first digital signal and a second digital signal indicatinga polarity of the input voltage, a potential of the first digital signalbeing opposite to that of the second digital signal; and a signalconversion circuit, for receiving at least one inductive signalreflecting an inductive voltage of the inductor, the first digitalsignal and the second digital signal and generating an analog signal; afeedback circuit, for receiving the analog signal and a predeterminedpulse signal, and generating a driving pulse signal; and a pulsedistribution circuit, for distributing the driving pulse signal to thefirst switch and the second switch of the first bridge arm according tothe first digital signal and the second digital signal so that one ofthe first switch and the second switch performs an ON operation,wherein, after a switch cycle, one of the first switch and the secondswitch performs the ON operation for a next switch cycle when a currentflowing through the inductor decreases to a predetermined thresholdvalue, and an ON time of the first switch is equal in each switch cycle,and an ON time of the second switch is equal in each switch cycle. 2.The control circuit of claim 1, wherein, the polarity detection circuitcomprises: a first operational amplifier, having a first input end, asecond input end and an output end, the first input end and the secondinput end of the first operational amplifier being connected to two endsof the input voltage respectively, and the output end of the firstoperational amplifier being used to output a voltage signal reflectingthe polarity of the input voltage; a first comparator, having a firstinput end, a second input end and an output end, the first input end ofthe first comparator being coupled to the output end of the firstoperational amplifier, the second input end of the first comparatorbeing coupled to a first reference voltage, the output end of the firstcomparator being used to output the first digital signal; and a firstinverter, for converting the first digital signal into the seconddigital signal.
 3. The control circuit of claim 1, wherein, the controlcircuit comprises a first auxiliary winding and a second auxiliarywinding both coupled to the inductor, and a polarity of a firstinductive signal generated by the first auxiliary winding is opposite tothat of a second inductive signal generated by the second auxiliarywinding.
 4. The control circuit of claim 3, wherein, the signalconversion circuit comprises: a first analog switch, having: a firstresistor, one end of the first resistor being connected to a first endof the first auxiliary winding; a third diode, an anode of the thirddiode being connected to the other end of the first resistor, a cathodeof the third diode being connected to an output end of the signalconversion circuit to output the analog signal; and a first switch, afirst end of the first switch being connected to the other end of thefirst resistor and the anode of the third diode, a second end of thefirst switch being connected to a ground end, and the control end of thefirst switch being used to receive the second digital signal; and asecond analog switch, having: a second resistor, one end of the secondresistor being connected to a first end of the second auxiliary winding,the second ends of the second auxiliary winding and the first auxiliarywinding being connected to a ground end respectively; a fourth diode, ananode of the fourth diode being connected to the other end of the secondresistor, a cathode of the fourth diode being connected to the outputend of the signal conversion circuit to output the analog signal; and asecond switch, a first end of the second switch being connected to theother end of the second resistor and the anode of the fourth diode, asecond end of the second switch being connected to a ground end, and acontrol end of the second switch being used to receive the first digitalsignal.
 5. The control circuit of claim 3, wherein, the signalconversion circuit comprises: a first analog switch, having: a fifthresistor, one end of the fifth resistor being connected to the first endof the first auxiliary winding; a third switch, a first end of the thirdswitch being connected to the first end of the first auxiliary winding,a second end of the third switch being connected to an anode of aseventh diode, and a control end of the third switch being connected tothe other end of the fifth resistor; and a fifth switch, a first end ofthe fifth switch being connected to the other end of the fifth resistorand the control end of the third switch, a second end of the fifthswitch being connected to a ground end, and a control end of the fifthswitch being used to receive the first digital signal; and a secondanalog switch, having: a sixth resistor, one end of the sixth resistorbeing connected to the first end of the second auxiliary winding, thesecond ends of the second auxiliary winding and the first auxiliarywinding being connected to a ground end respectively; a fourth switch, afirst end of the fourth switch being connected to the first end of thesecond auxiliary winding, a second end of the fourth switch beingconnected to an anode of an eighth diode, and a control end of thefourth switch being connected to the other end of the sixth resistor;and a sixth switch, a first end of the sixth switch being connected tothe other end of the sixth resistor and the control end of the fourthswitch, a second end of the sixth switch being connected to a groundend, a control end of the sixth switch being used to receive the seconddigital signal, and the cathodes of the seventh diode and the eighthdiode being connected to the output end of the signal conversion circuitrespectively to output the analog signal.
 6. The control circuit ofclaim 1, wherein, the control circuit comprises a third auxiliarywinding coupled to the inductor, and the analog signal is generatedthrough a third inductive signal generated by the third auxiliarywinding, the first digital signal and the second digital signal.
 7. Thecontrol circuit of claim 6, wherein, the signal conversion circuitcomprises: a first analog switch, having: a seventh resistor, one end ofthe seventh resistor being connected to a first end of the thirdauxiliary winding; a ninth diode, an anode of the ninth diode beingconnected to the other end of the seventh resistor, a cathode of theninth diode being connected to the output end of the signal conversioncircuit to output the analog signal; and a seventh switch, a first endof the seventh switch being connected to the other end of the seventhresistor and the anode of the ninth diode, a second end of the seventhswitch being connected to a ground end, and a control end of the seventhswitch being used to receive the second digital signal; and a secondanalog switch, having: an eighth resistor, one end of the eighthresistor being connected to a second end of the third auxiliary winding;a tenth diode, an anode of the tenth diode being connected to the otherend of the eighth resistor, a cathode of the tenth diode being connectedto the output end of the signal conversion circuit to output the analogsignal; and an eighth switch, a first end of the eighth switch beingconnected to the other end of the eighth resistor and the anode of thetenth diode, a second end of the eighth switch being connected to aground end, and a control end of the eighth switch being used to receivethe first digital signal.
 8. The control circuit of claim 1, wherein,the feedback circuit comprises: a second operational amplifier, having afirst input end, a second input end and an output end, the first inputend of the second operational amplifier being used to receive an outputvoltage of the PFC circuit, the second input end of the secondoperational amplifier being coupled to a second reference voltage, andthe output end of the second operational amplifier outputting adifference amplification signal; a second comparator, having a firstinput end, a second input end and an output end, the first input end ofthe second comparator being coupled to the output end of the secondoperational amplifier, the second input end of the second comparatorbeing used to receive a saw-tooth wave voltage signal, the output end ofthe second comparator outputting the predetermined pulse signal; and aRS trigger, having a preset end, a reset end and an output end, thepreset end of the RS trigger being used to receive the analog signalfrom the signal conversion circuit, the reset end of the RS triggerbeing used to receive the predetermined pulse signal from the secondcomparator, and the output end of the RS trigger being used to outputthe driving pulse signal.
 9. The control circuit of claim 8, wherein,the feedback circuit further comprises a delay circuit arranged betweenthe signal conversion circuit and the RS trigger, and the delay circuitis used to delay the analog signal and send the delayed analog signal tothe preset end of the RS trigger.
 10. The control circuit of claim 9,wherein, the feedback circuit further comprises a comparing unitarranged between the delay circuit and the RS trigger, and the comparingunit is used to convert the delayed analog signal into a correspondingdigital delay signal and send it to the preset end of the RS trigger.11. The control circuit of claim 1, wherein, the pulse distributioncircuit comprises: a first AND gate circuit, having a first input end, asecond input end and an output end, the first input end of the first ANDgate circuit being used to receive the first digital signal, the secondinput end of the first AND gate circuit being used to receive thedriving pulse signal, and the output end of the first AND gate circuitoutputting a first control signal to the first switch of the firstbridge arm; and a second AND gate circuit, having a first input end, asecond input end and an output end, the first input end of the secondAND gate circuit being used to receive the second digital signal, thesecond input end of the second AND gate circuit being used to receivethe driving pulse signal, and the output end of the second AND gatecircuit outputting a second control signal to the second switch of thefirst bridge arm.
 12. The control circuit of claim 11, wherein, when thepolarity of the input voltage is positive, the first digital signal isat a low potential and the second digital signal is at a high potential;and when the polarity of the input voltage is negative, the firstdigital signal is at a high potential and the second digital signal isat a low potential.
 13. A power source system, comprising: a PFCcircuit, comprising: a first bridge arm, comprising a first switch and asecond switch connected with each other in series, a common node of thefirst switch and the second switch being coupled to one end of an inputvoltage through an inductor; and a second bridge arm, comprising a thirdswitch and a fourth switch connected with each other in series, a commonnode of the third switch and the fourth switch being coupled to theother end of the input voltage; and a control circuit, comprising a zerocurrent detection circuit, having a polarity detection circuit and asignal conversion circuit, wherein, the polarity detection circuit isused to receive the input voltage and output a first digital signal anda second digital signal indicating a polarity of the input voltage, apotential of the first digital signal is opposite to that of the seconddigital signal, and the signal conversion circuit is used to receive atleast one inductive signal reflecting an inductive voltage of theinductor, the first digital signal and the second digital signal, andgenerate an analog signal; a feedback circuit, for receiving the analogsignal and a predetermined pulse signal, and generating a driving pulsesignal; and a pulse distribution circuit, for distributing the drivingpulse signal to the first switch and the second switch of the firstbridge arm according to the first digital signal and the second digitalsignal so that one of the first switch and the second switch performs anON operation, wherein, after a switch cycle, one of the first switch andthe second switch performs the ON operation for a next switch cycle whena current flowing through the inductor decreases to a predeterminedthreshold value, and an ON time of the first switch is equal in eachswitch cycle, and an ON time of the second switch is equal in eachswitch cycle.
 14. The power source system of claim 13, wherein, thecontrol circuit comprises a first auxiliary winding and a secondauxiliary winding both coupled to the inductor, and a polarity of afirst inductive signal generated by the first auxiliary winding isopposite to that of a second inductive signal generated by the secondauxiliary winding.
 15. The power source system of claim 13, wherein, thecontrol circuit comprises a third auxiliary winding coupled to theinductor, and the analog signal is generated by a third inductive signalgenerated by the third auxiliary winding, the first digital signal andthe second digital signal.
 16. The power source system of claim 13,wherein, each of the first switch and the second switch in the firstbridge arm is a fast-recovery MOSFET and each of the third switch andthe fourth switch in the second bridge arm is a slow-recovery MOSFET.17. The power source system of claim 16, wherein, each of the firstswitch and the second switch is a wide band gap semiconductor component.18. The power source system of claim 17, wherein, the wide band gapsemiconductor component is silicon carbide or gallium nitride.
 19. Acontrol method for a PFC circuit, wherein the PFC circuit comprises aninductor, a first bridge arm and a second bridge arm connected to thefirst bridge arm in parallel, the first bridge arm having a first switchand a second switch connected with each other in series, a common nodeof the first switch and the second switch being coupled to an inputvoltage through the inductor, and the control method comprises:detecting a polarity of the input voltage to output a first digitalsignal and a second digital signal indicating the polarity of the inputvoltage; generating an analog signal through a signal conversionprocessing according to at least one inductive signal reflecting aninductive voltage of the inductor, the first digital signal and thesecond digital signal; providing a predetermined pulse signal andgenerating a driving pulse signal according to the analog signal and thepredetermined pulse signal; and distributing the driving pulse signal tothe first switch and the second switch according to the first digitalsignal and the second digital signal so that one of the first switch andthe second switch performs an ON operation.
 20. The control method ofclaim 19, wherein, after a switch cycle, one of the first switch and thesecond switch performs the ON operation for the next switch cycle when acurrent flowing through the inductor decreases to a predeterminedthreshold value, and an ON time of the first switch is equal in eachswitch cycle, and an ON time of the second switch is equal in eachswitch cycle.
 21. The control method of claim 19, wherein, the step ofdetecting a polarity of the input voltage further comprises: performinga difference amplification for the input voltage to obtain a voltagesignal reflecting the polarity of the input voltage; comparing thevoltage signal with a first reference voltage to obtain and output thefirst digital signal; and reversing the first digital signal to obtainand output the second digital signal.
 22. The control method of claim19, wherein, the step of providing a predetermined pulse signal andgenerating a driving pulse signal further comprises: performing anamplification of difference between an output voltage of the PFC circuitand a second reference voltage to output a difference amplificationsignal; comparing the difference amplification signal with a saw-toothwave voltage signal to output the predetermined pulse signal; andinputting the analog signal and the predetermined pulse signal into apreset end and a reset end of a RS trigger respectively and outputtingthe driving pulse signal through the RS trigger.
 23. The control methodof claim 22, wherein, the step of providing a predetermined pulse signaland generating a driving pulse signal further comprises: performing adelay processing for the analog signal and sending the delayed analogsignal to the preset end of the RS trigger.
 24. The control method ofclaim 19, wherein, the step of distributing the driving pulse signal tothe first switch and the second switch further comprises: performing alogic AND operation for the first digital signal and the driving pulsesignal and sending a processed first control signal to a control end ofthe first switch; and performing the logic AND operation for the seconddigital signal and the driving pulse signal and sending a processedsecond control signal to a control end of the second switch, wherein,one of the first switch and the second switch is enabled to perform theON operation correspondingly by one of the first control signal and thesecond control signal.